Bryce Vickmark for The New York Times

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That’s because Dr. Lieberman, an evolutionary biology professor atHarvard, spends his time studying how the human head and foot have evolved over the millenniums. In January, Harvard University Press published his treatise, “The Evolution of the Human Head.”

We spoke in a Cambridge hotel room for three hours last winter and then again on the telephone in June. An edited and condensed version of the two conversations follows.

Q. Why heads?

A. Our heads are what make our species interesting. If you were to meet a Neanderthal or a Homo erectus, you’d see that they are the same as us — except from the neck up. We’re different in our noses, ears, teeth, how we swallow and chew. When you think about what makes us human, it’s our big brains, complex thought and language. We speak with our heads, breathe and smell with our heads. So understanding how we got these heads is vital for knowing who we are and what we are doing on this planet.

Q. Are there any practical benefits to your research?

A. There are. A majority of the undergraduates who register for my evolutionary anatomy and physiology class here at Harvard are pre-medical students. Learning this will help them become better doctors. Many of the conditions they’ll be treating are rooted in the mismatch between the world we live in today and the Paleolithic bodies we’ve inherited.

For example, impacted wisdom teeth and malocclusions are very recent problems. They arise because we now process our food so much that we chew with little force. These interactions affect how our faces grow, which causes previously unknown dental problems. Hunter-gatherers — who live in ways similar to our ancestors — don’t have impacted wisdom teeth or cavities. There are many other conditions rooted in the mismatch — fallen arches, osteoporosis, cancer, myopia, diabetes and back trouble. So understanding evolutionary biology will definitely help my students when they become orthopedists, orthodontists and craniofacial surgeons.

Q. Your other specialty is the evolution of the foot. Why this emphasis on the farthest points of our bodies?

A. Actually, I’m interested in the entire body. However, I got into feet because of my interest in heads. Some years ago, I was doing an experiment where I put pigs on treadmills. The goal was to learn how running stressed the bones in the head. One day, a colleague, Dennis Bramble, walked into the lab, watched what was going on, and declared, “You know, that pig can’t hold its head still!”

This was my “eureka!” moment. I’d observed pigs on treadmills for hundreds of hours and had never thought about this. So Dennis and I started talking about how, when these pigs ran, their heads bobbed every which way and how running humans are really adept at stabilizing their heads. We realized that there were special features in the human neck that enable us to keep our heads still. That gives us an evolutionary advantage because it helps us avoid falls and injuries. And this seemed like evidence of natural selection in our ability to run, an important factor in how we became hunters rather than just foragers and got access to richer foods, which fueled the evolution of our big brains.

So I got interested in how we developed these stable heads. I’m a runner myself. It’s always interesting to study one’s passion. By 2004, we’d found enough evidence to publish a paper in Nature where we declared, “Humans were born to run.” We cited the many dozens of adaptations in the human body that had made us into superlative endurance runners, even compared to dogs and horses.

Before bows and arrows and before horses were tamed, we did “persistence hunting” where we ran kudu, wildebeest and zebra into exhaustion. These animals can’t pant when they gallop. They overheat. People would find a big animal and chase it till it collapsed. You need no technology to do this, just the ability to run long distances, which all of us have.

You can see proof of this capability every November when 45,000 people run for many hours through the streets of New York.

Q. People with bad backs often blame evolution for their pain. They say, “My back aches because man was not meant to walk on two feet.” Are they right?

A. If that were true, natural selection would have its toll and we’d be extinct. What is more likely is that many people sit in chairs all day, get no exercise, and thus have weak backs. We did not evolve to sit in chairs all day.

Q. In your lab, you study the phenomenon of barefoot running. How did that become part of your portfolio?